My family's dark Somme secret, by TV historian
Delving into his own ancestors' past, Dan Snow was stunned to discover that his great-grandfather was a first world war general who sent thousands to die

Dan Snow, the TV historian, belongs to one of Britain's most distinguished broadcasting families. When he began looking into the past of a little-known ancestor, however, he was shocked to uncover a deeply uncomfortable family secret. Sir Thomas D'Oyly Snow, the grandfather of TV journalists Peter and Jon Snow, was a general at the Battle of the Somme who sent thousands of men to their deaths.

Dan came close to tears as he stood in the graveyards of northern France, contemplating his great-grandfather's central role in the biggest disaster in British military history. On the first day at the Somme, 1 July 1916, the army suffered 57,470 casualties, including 19,240 dead. Popular history would judge that these men were 'lions' led by 'donkeys' such as Douglas Haig and Thomas Snow. 'That is the darkest day in British military history, arguably British history, and my great-grandpa was one of the key guys in the planning and execution of that attack,' Dan Snow told The Observer last week. 'That was a huge surprise. It's fascinating to be descended from one of the most maligned men in British history.'

Dan is the son of Peter Snow, the former Newsnight presenter famed for the election night 'swingometer', and together they presented the TV series Battlefield Britain. Peter is a cousin of Jon Snow, the main presenter of Channel 4 News. Dan's grandfathers both fought in the Second World War, one in the army in India, the other in the Canadian navy. But despite being a professional historian Dan had not examined his own family history. He grew up aware of Thomas from a portrait on the living-room wall and his father's joking description of him as 'a bit rubbish'. 'He had a very stern face and this big moustache,' said Dan. 'He used to stare down at us from the wall as we ate.'

So the historian seized the BBC's offer to take part in My Family at War, a series in which celebrities trace ancestors connected with the First World War to mark next month's 90th anniversary of the Armistice. But unlike many of the other participants, who include Rolf Harris and Kirsty Wark, Dan did not find a straightforward story of lost innocence.

The research made for a harrowing journey for Dan, 29, who confessed to feeling a mixture of pride and shame in his ancestor. Thomas, a soldier since 1879, was a veteran of the Zulu War in South Africa and the doomed attempt to relieve Charles Gordon in Khartoum during the war against the Mahdi. When conflict broke out in 1914 he was a divisional commander and saw action at the Marne and Ypres, suffering a serious injury after falling from his horse. On the first day of the Battle of the Somme, he commanded VII Corps in an attack on Gommecourt which ended in failure.

Dan retraced his great-grandfather's movements in the programme, to be shown on BBC1 at 10.35pm on 3 November. 'It was quite jarring,' he recalled. 'I went to the ch‚teau he was in on the first day of the Somme. The sun was pouring in through the window and I was sitting at his desk. He said when the wind was right he could just about hear the artillery; a few miles away from him the most bloody slaughter in British history was going on. Obviously it was very disturbing, but it's too easy to make trite conclusions and say he was a complete scoundrel for not sharing the dangers with his men. That's not why he was being paid. He was actually being paid to try to work out what the hell was going on and how he was going to overcome these problems.' But in one of his least edifying acts, Thomas Snow apparently sought to pass blame for his part in the debacle to one of his subordinates.

He wrote to headquarters: 'I regret to have to report that the 46th Division in yesterday's operation showed a lack of offensive spirit. I can only attribute this to the fact that its commander, Maj Gen the Hon E J Stuart-Wortley, is not of an age, neither has he the constitution, to allow him to be as much among his men in the front lines as is necessary to imbue all ranks with confidence and spirit. I therefore recommend that a younger man, and one more physically capable of energy, should be appointed to command the division.'

Stuart-Wortley was consequently sacked by Haig and spent the next eight years striving to clear his name. Dan described his great-grandfather's behaviour in the incident as 'unacceptable'. He said: 'You can imagine the upper echelons of the British army, everybody blaming each other. It was chaos. Everyone was trying to save their skin and he blamed the group that couldn't answer back and that was the dead. That was a very difficult moment for me.'

Yet Dan, who has studied the First World War, refused to condemn Thomas and his peers unequivocally. 'I think the lions led by donkeys thing is untrue. Obviously there were total duds among the generals, but on the whole they were a very bright group of men struggling with some of the biggest challenges ever posed in warfare. The rulebook had been ripped up and thrown away, and they were dealing with an entirely different kind of warfare, technologies and world. It was incredibly difficult and they adapted to the industrial warfare of the First World War quicker than the Americans adapted to guerrilla warfare in Iraq.' He added: 'It's such an interesting story that it's impossible to have one overwhelming emotion. You feel a huge mixture of a bit of pride, on one or two occasions shame when he had made big mistakes, and on a lot of other occasions simply pity. It's difficult for us to judge.'

Jon Snow said he had not dwelt on his grandfather's decisions at the Somme: 'The First World War I have written off as a dark chapter for all concerned. For Tom, probably, a darker chapter in terms of his responsibility than one would wish. But I prefer to remember him for going to the relief of Khartoum. He brought a part of the step on which Gordon died back to Britain and it sat on the mantelpiece of his home in Kensington Gate until the Blitz in 1941, when the house was demolished and nobody was able to distinguish the old stone from the rest of the rubble.'